Construction structures and manufacturing processes for integrated circuit wafer probe card assemblies

ABSTRACT

Several embodiments of integrated circuit probe card assemblies are disclosed, which extend the mechanical compliance of both MEMS and thin-film fabricated probes, such that these types of spring probe structures can be used to test one or more integrated circuits on a semiconductor wafer. Several embodiments of probe card assemblies, which provide tight signal pad pitch compliance and/or enable high levels of parallel testing in commercial wafer probing equipment, are disclosed. In some preferred embodiments, the probe card assembly structures include separable standard components, which reduce assembly manufacturing cost and manufacturing time. These structures and assemblies enable high speed testing in wafer form. The probes also have built in mechanical protection for both the integrated circuits and the MEMS or thin film fabricated spring tips and probe layout structures on substrates. Interleaved spring probe tip designs are defined which allow multiple probe contacts on very small integrated circuit pads. The shapes of probe tips are preferably defined to control the depth of probe tip penetration between a probe spring and a pad or trace on an integrated circuit device. Improved protective coating techniques for spring probes are also disclosed, offering increased reliability and extended useful service lives for probe card assemblies.

CLAIM FOR PRIORITY

This application claims priority from PCT Internatonal ApplicationNumber PCT/US00/21012, filed 28 Jul. 2000, which claims priority fromU.S. Provisional Application 60/146,241, filed Jul. 28, 1999.

FIELD OF THE INVENTION

The invention relates to the field of probe card assembly systems. Moreparticularly, the invention relates to improvements inphotolithography-patterned spring contacts and enhanced probe cardassemblies having photolithography-pattemed spring contacts for use inthe testing or burn-in of integrated circuits.

BACKGROUND OF THE INVENTION

In conventional integrated circuit (IC) wafer probe cards, electricalcontacts between the probe card and an integrated circuit wafer aretypically provided by tungsten needle probes. However, advancedsemiconductor technologies often require higher pin counts, smaller padpitches, and higher clock frequencies, which are not possible withtungsten needle probes.

While emerging technologies have provided spring probes for differentprobing applications, most probes have inherent limitations, such aslimited pitch, limited pin count, varying levels of flexibility, limitedprobe tip geometries, limitations of materials, and high costs offabrication.

K. Banerji, A. Suppelsa, and W. Mullen III, Selectively ReleasingConductive Runner and Substrate Assembly Having Non-Planar Areas, U.S.Pat. No. 5,166,774 (24 Nov. 1992) disclose a runner and substrateassembly which comprises “a plurality of conductive runners adhered to asubstrate, a portion of at least some of the conductive runners havenon-planar areas with the substrate for selectively releasing theconductive runner from the substrate when subjected to a predeterminedstress”.

A. Suppelsa, W. Mullen III and G. Urbish, Selectively ReleasingConductive Runner and Substrate Assembly, U.S. Pat. No. 5,280,139 (18Jan. 1994) disclose a runner and substrate assembly which comprises “aplurality of conductive runners adhered to a substrate, a portion of atleast some of the conductive runners have a lower adhesion to thesubstrate for selectively releasing the conductive runner from thesubstrate when subjected to a predetermined stress”.

D. Pedder,Bare Die Testing, U.S. Pat. No. 5,786,701 (28 Jul. 1998)disclose a testing apparatus for testing integrated circuits (ICs) atthe bare die stage, which includes “a testing station at whichmicrobumps of conductive material are located on interconnection traceterminations of a multilayer interconnection structure, theseterminations being distributed in a pattern corresponding to the patternof contact pads on the die to be tested. To facilitate testing of thedie before separation from a wafer using the microbumps, the otherconnections provided to and from the interconnection structure have alow profile”.

D. Grabbe, I. Korsunsky and R. Ringler, Surface Mount ElectricalConnector, U.S. Pat. No. 5,152,695 (6 Oct. 1992) disclose a connectorfor electrically connecting a circuit between electronic devices, inwhich “the connector includes a platform with cantilevered spring armsextending obliquely outwardly therefrom. The spring arms include raisedcontact surfaces and in one embodiment, the geometry of the arms providecompound wipe during deflection”.

H. Iwasaki, H. Matsunaga, and T. Ohkubo, Partly Replaceable Device forTesting a Multi-Contact Integrated Circuit Chip Package, U.S. Pat. No.5,847,572 (8 Dec. 1998) disclose “a test device for testing anintegrated circuit (IC) chip having side edge portions each providedwith a set of lead pins. The test device comprises a socket base,contact units each including a contact support member and socket contactnumbers, and anisotropic conductive sheet assemblies each including anelastic insulation sheet and conductive members. The anisotropicconductive sheet assemblies are arranged to hold each conductive memberin contact with one of the socket contact members of the contact units.The test device further comprises a contact retainer detachably mountedon the socket base to bring the socket contact members into contact withthe anisotropic sheet assemblies to establish electrical communicationbetween the socket contact members and the conductive members of theanisotropic conductive sheet assemblies. Each of the contact units canbe replaced by a new contact unit if the socket contact members partlybecome fatigued, thereby making it possible to facilitate themaintenance of the test device. Furthermore, the lead pins of the ICchip can be electrically connected to a test circuit board with theshortest paths formed by part of the socket contact members and theconductive members of the anisotropic conductive sheet assemblies”.

W. Berg, Method of Mounting a Substrate Structure to a Circuit Board,U.S. Pat. No. 4,758,9278 (19 Jul. 1988) discloses “a substrate structurehaving contact pads is mounted to a circuit board which has pads ofconductive material exposed at one main face of the board and hasregistration features which are in predetermined positions relative tothe contact pads of the circuit board. The substrate structure isprovided with leads which are electrically connected to the contact padsof the substrate structure and project from the substrate structure incantilever fashion. A registration element has a plate portion and alsohas registration features which are distributed about the plate portionand are engageable with the registration features of the circuit board,and when so engaged, maintain the registration element against movementparallel to the general plane of the circuit board. The substratestructure is attached to the plate portion of the registration elementso that the leads are in predetermined position relative to theregistration features of the circuit board, and in this position of theregistration element the leads of the substrate structure overlie thecontact pads of the circuit board. A clamp member maintains the leads inelectrically conductive pressure contact with the contact pads of thecircuit board”.

D. Sarma, P. Palanisamy, J. Hearn and D. Schwarz, Controlled AdhesionConductor, U.S. Pat. No. 5,121,298 (9 Jun. 1992) disclose “Compositionsuseful for printing controllable adhesion conductive patterns on aprinted circuit board include finely divided copper powder, a screeningagent and a binder. The binder is designed to provide controllableadhesion of the copper layer formed after sintering to the substrate, sothat the layer can lift off the substrate in response to thermal stress.Additionally, the binder serves to promote good cohesion between thecopper particles to provide good mechanical strength to the copper layerso that it can tolerate lift off without fracture”.

R. Mueller, Thin-Film Electrothermal Device, U.S. Pat. No. 4,423,401 (27Dec. 1983) discloses “A thin film multilayer technology is used to buildmicro-miniature electromechanical switches having low resistancemetal-to-metal contacts and distinct on-off characteristics. Theswitches, which are electrothermally activated, are fabricated onconventional hybrid circuit substrates using processes compatible withthose employed to produce thin-film circuits. In a preferred form, sucha switch includes a cantilever actuator member comprising a resilientlybendable strip of a hard insulating material (e.g. silicon nitride) towhich a metal (e.g. nickel) heating element is bonded. The free end ofthe cantilever member carries a metal contact, which is moved onto (orout on engagement with an underlying fixed contact by controlled bendingof the member via electrical current applied to the heating element”.

S. Ibrahim and J. Elsner, Multi-Layer Ceramic Package, U.S. Pat. No.4,320,438 (16 Mar. 1982) disclose “In a multi-layer package, a pluralityof ceramic lamina each has a conductive pattern, and there is aninternal cavity of the package within which is bonded a chip or aplurality of chips interconnected to form a chip array. The chip or chiparray is connected through short wire bonds at varying lamina levels tometallized conductive patterns thereon, each lamina level having aparticular conductive pattern. The conductive patterns on the respectivelamina layers are interconnected either by tunneled through openingsfilled with metallized material, or by edge formed metallizations sothat the conductive patterns ultimately connect to a number of pads atthe undersurface of the ceramic package mounted onto a metalized board.There is achieved a high component density; but because connecting leadsare “staggered” or connected at alternating points with wholly differentpackage levels, it is possible to maintain a 10 mil spacing and 10 milsize of the wire bond lands. As a result, there is even greatercomponent density but without interference of wire bonds one with theother, this factor of interference being the previous limiting factor inachieving high component density networks in a multi-layer ceramicpackage”.

F. McQuade, and J. Lander, Probe Assembly for Testing IntegratedCircuits, U.S. Pat. No. 5,416,429 (16 May 1995) disclose a probeassembly for testing an integrated circuit, which “includes a probe cardof insulating material with a central opening, a rectangular frame witha smaller opening attached to the probe card, four separate probe wingseach comprising a flexible laminated member having a conductive groundplane sheet, an adhesive dielectric film adhered to the ground plane,and probe wing traces of spring alloy copper on the dielectric film.Each probe wing has a cantilevered leaf spring portion extending intothe central opening and terminates in a group of aligned individualprobe fingers provided by respective terminating ends of said probe wingtraces. The probe fingers have tips disposed substantially along astraight line and are spaced to correspond to the spacing of respectivecontact pads along the edge of an IC being tested. Four spring clampseach have a cantilevered portion which contact the leaf spring portionof a respective probe wing, so as to provide an adjustable restraint forone of the leaf spring portions. There are four separate spring clampadjusting means for separately adjusting the pressure restraintsexercised by each of the spring clamps on its respective probe wing. Theseparate spring clamp adjusting means comprise spring biased platformseach attached to the frame member by three screws and spring washers sothat the spring clamps may be moved and oriented in any desireddirection to achieve alignment of the position of the probe finger tipson each probe wing”.

D. Pedder, Structure for Testing Bare Integrated Circuit Devices,European Patent Application No. EP 0 731 369 A2 (Filed 14 Feb. 1996),U.S. Pat. No. 5,764,070 (9 Jun. 1998) discloses a test probe structurefor making connections to a bare IC or a wafer to be tested, whichcomprises “a multilayer printed circuit probe arm which carries at itstip an MCM-D type substrate having a row of microbumps on its undersideto make the required connections. The probe arm is supported at ashallow angle to the surface of the device or wafer, and the MCM-D typesubstrate is formed with the necessary passive components to interfacewith the device under test. Four such probe arms may be provided, one oneach side of the device under test”.

B. Eldridge, G. Grube, I. Khandros, and G. Mathieu, Method of MountingResilient Contact Structure to Semiconductor Devices, U.S. Pat. No.5,829,128 (3 Nov. 1998), Method of Making Temporary Connections BetweenElectronic Components, U.S. Pat. No. 5,832,601 (10 Nov. 1998), Method ofMaking Contact Tip Structures, U.S. Pat. No. 5,864,946 (2 Feb. 1999),Mounting Spring Elements on Semiconductor Devices, U.S. Pat. No.5,884,398 (23 Mar. 1999), Method of Burning-In Semiconductor Devices,U.S. Pat. No. 5,878,486 (9 Mar. 1999), and Method of ExercisingSemiconductor Devices, U.S. Pat. No. 5,897,326 (27 Apr. 1999), disclose“Resilient contact structures are mounted directly to bond pads onsemiconductor dies, prior to the dies being singulated (separated) froma semiconductor wafer. This enables the semiconductor dies to beexercised (e.g. tested and/or burned-in) by connecting to thesemiconductor dies with a circuit board or the like having a pluralityof terminals disposed on a surface thereof. Subsequently, thesemiconductor dies may be singulated from the semiconductor wafer,whereupon the same resilient contact structures can be used to effectinterconnections between the semiconductor dies and other electroniccomponents (such a wiring substrates, semiconductor packages, etc.).Using the all-metallic composite interconnection elements of the presentinvention as the resilient contact structures, burn-in can be performedat temperatures of at least 150° C., and can be completed in less than60 minutes”. While the contact tip structures disclosed by B. Eldridgeet al. provide resilient contact structures, the structures are eachindividually mounted onto bond pads on semiconductor dies, requiringcomplex and costly fabrication. As well, the contact tip structures arefabricated from wire, which often limits the resulting geometry for thetips of the contacts. Furthermore, such contact tip structures have notbeen able to meet the needs of small pitch applications (e.g. typicallyon the order of 50 μm spacing for a peripheral probe card, or on theorder of 75 μm spacing for an area array).

T. Dozier II, B. Eldridge, G. Grube, I. Khandros, and G. Mathieu,Sockets for Electronic Components and Methods of Connecting toElectronic Components, U.S. Pat. No. 5,772,451 (30 Jun. 1998) disclose“Surface-mount, solder-down sockets permit electronic components such assemiconductor packages to be releasably mounted to a circuit board.Resilient contact structures extend from a top surface of a supportsubstrate, and solder-ball (or other suitable) contact structures aredisposed on a bottom surface of the support substrate. Compositeinterconnection elements are used as the resilient contact structuresdisposed atop the support substrate. In any suitable manner, selectedones of the resilient contact structures atop the support substrate areconnected, via the support substrate, to corresponding ones of thecontact structures on the bottom surface of the support substrate. In anembodiment intended to receive an LGA-type semiconductor package,pressure contact is made between the resilient contact structures andexternal connection points of the semiconductor package with a contactforce which is generally normal to the top surface of the supportsubstrate. In an embodiment intended to receive a BGA-type semiconductorpackage, pressure contact is made between the resilient contactstructures and external connection points of the semiconductor packagewith a contact force which is generally parallel to the top surface ofthe support substrate”.

Other emerging technologies have disclosed probe tips on springs whichare fabricated in batch mode processes, such as by thin-film or microelectronic mechanical system (MEMS) processes.

D. Smith and S. Alimonda, Photolithographically Patterned SpringContact, U.S. Pat. No. 5,613,861 (25 Mar. 1997), U.S. Pat. No. 5,848,685(15 Dec. 1998), and International Patent Application No. PCT/US 96/08018(Filed 30 May 1996), disclose a photolithography patterned springcontact, which is “formed on a substrate and electrically connectscontact pads on two devices. The spring contact also compensates forthermal and mechanical variations and other environmental factors. Aninherent stress gradient in the spring contact causes a free portion ofthe spring to bend up and away from the substrate. An anchor portionremains fixed to the substrate and is electrically connected to a firstcontact pad on the substrate. The spring contact is made of an elasticmaterial and the free portion compliantly contacts a second contact pad,thereby contacting the two contact pads”. While the photolithographypatterned springs, as disclosed by Smith et al., are capable ofsatisfying many IC probing needs, the springs are small, and providelittle vertical compliance to handle the planarity compliance needed inthe reliable operation of many current IC prober systems. Verticalcompliance for many probing systems is typically on the order of0.004″-0.010″, which often requires the use of tungsten needle probes.

Furthermore, no one has taught a way to interconnect such a probecontaining up to several thousand pins to a tester, while effectivelydealing with planarity requirements. As advanced integrated circuitdevices become more complex while decreasing in size, it would beadvantageous to provide a probe card assembly which can be used toreliably interconnect to such devices.

To accommodate for planarity differences between an array of probe tipsand the surface pads on a wafer under test, it may be advantageous toprovide a probe substrate which can pivot freely by a small amount aboutits center. For such a system, however, an accurately controlled forcemust still be provided to engage the contacts, while holding thesubstrate positionally stable in the X, Y, and theta directions.Furthermore, for applications in which the substrate includes a largenumber (e.g. thousands) of wires or signals exiting its backside,wherein supports are located at the periphery of the substrate, thesesupports must not hinder the fan-out exit pathways. As well, the signalwires must not hinder the pivoting of the substrate, nor should theyhinder the controlled force provided to engage the springs against adevice under test (DUT).

It would be advantageous to provide a method and apparatus for improvedflexible probe springs, which are capable of high pin counts, smallpitches, cost-effective fabrication, and customizable spring tips. Itwould also be advantageous to provide probe card assemblies using suchflexible probe springs, which provide planarity compliance tosemiconductor devices under testing and/or burn-in, while providingaccurate axial and theta positioning.

SUMMARY OF THE INVENTION

Several embodiments of integrated circuit probe card assemblies aredisclosed, which extend the mechanical compliance of both MEMS andthin-film fabricated probes, such that these types of spring probestructures can be used to test one or more integrated circuits on asemiconductor wafer. Several embodiments of probe card assemblies aredisclosed, which provide tight signal pad pitch and compliance,preferably enabling the parallel testing or burn-in of multiple ICs,using commercial wafer probing equipment. In some preferred embodiments,the probe card assembly structures include separable standard electricalconnector components, which reduces assembly manufacturing cost andmanufacturing time. These structures and assemblies enable high speedtesting of IC's in wafer form, as well as high density substrates. Theprobes preferably include mechanical protection for both the integratedcircuits and the MEMS or thin film fabricated spring tips. Interleavedspring probe tip designs are defined which allow multiple probe contactson very small integrated circuit pads. The shapes of probe tips arepreferably defined to control the depth of probe tip penetration betweena probe spring and a pad or trace on an integrated circuit device.Improved protective coating techniques for spring probes are alsodisclosed, offering increased quality and extended useful service livesfor probe card assemblies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a linear array of photolithographicallypatterned springs, prior to release from a substrate;

FIG. 2 is a perspective view of a linear array of photolithographicallypatterned springs, after release from a substrate;

FIG. 3 is a side view of a first, short length photolithographicallypatterned spring, having a first effective radius and height after theshort length spring is released from a substrate;

FIG. 4 is a side view of a second, long length photolithographicallypatterned spring, having a second large effective radius and heightafter the long length spring is released from a substrate;

FIG. 5 is a perspective view of opposing photolithographic springs,having an interleaved spring tip pattern, before the springs arereleased from a substrate;

FIG. 6 is a perspective view of opposing photolithographic springs,having an interleaved spring tip pattern, after the springs are releasedfrom a substrate;

FIG. 7 is a top view of opposing pairs of interleaved multiple-pointphotolithographic probe springs, in contact with a single trace on anintegrated circuit device;

FIG. 8 is a plan view of opposing single-point photolithographic probesprings, before the springs are released from a substrate;

FIG. 9 is a top view of parallel and opposing single-pointphotolithographic probe springs, after the springs are released from asubstrate, in contact with a single pad on an integrated circuit device;

FIG. 10 is a front view of a shoulder-point photolithographic probespring;

FIG. 11 is a partial cross-sectional side view of a shoulder-pointphotolithographic spring in contact with a trace on an integratedcircuit device;

FIG. 12 is a perspective view of a multiple shoulder-pointphotolithographic probe spring;

FIG. 13 is a cross-sectional view of a probe card assembly, wherein aplurality of photolithographic spring probes on a lower surface of asubstrate are electrically connected to flexible connections on theupper surface of the substrate, and wherein the flexible connections areconnected to a printed wiring board probe card;

FIG. 14 is a partial expanded cross-sectional view of a probe cardassembly, which shows staged pitch and fan-out across a substrate and aprinted wiring board probe card;

FIG. 15 is a first partial cross-sectional view of a bridge and leafspring suspended probe card assembly;

FIG. 16 is a second partial cross-sectional view of a bridge and leafspring suspended probe card assembly in contact with a device under test(DUT);

FIG. 17 is a partially expanded assembly view of a bridge and leafspring suspended probe card assembly;

FIG. 18 is a first partial cross-sectional view of a bridge and leafspring suspended probe card assembly, having an intermediate daughtercard detachably connected to the probe card substrate, and wherein theprobe spring substrate is detachably connected to the bridge structure;

FIG. 19 is a second partial cross-sectional view of the bridge and leafspring suspended probe card assembly shown in contact with a deviceunder test (DUT);

FIG. 20 is a cross-sectional view of a wire and spring post suspendedprobe card assembly;

FIG. 21 is a cross-sectional view of a suspended probe card assemblyhaving an intermediate daughter card detachably connected to the probecard substrate, and wherein the probe spring substrate is mechanicallyand electrically connected to the bridge structure by flexibleinterconnections;

FIG. 22 is a cross-sectional view of a probe card assembly, wherein anano-spring substrate is directly connected to a probe card substrate byan array connector;

FIG. 23 is a cross-sectional view of a wire suspended probe cardassembly, wherein a nano-spring substrate is connected to a probe cardsubstrate by an LGA interposer connector;

FIG. 24 is a cross-sectional view of a small test area probe cardassembly, having one or more connectors between a probe card and adaughter card, in which the daughter card is attached to a small areaprobe spring substrate by a micro ball grid solder array;

FIG. 25 is a top view of a substrate wafer, upon which a plurality ofmicro ball grid array probe spring contactor chip substrates are laidout;

FIG. 26 is a top view of a single micro ball grid array nano-springcontactor chip;

FIG. 27 is a plan view of a probe strip tile having a plurality of probecontact areas;

FIG. 28 is a bottom view of a plurality of probe strip tiles attached toa probe card support substrate;

FIG. 29 is a side view of a plurality of probe strip tiles attached to aprobe card support substrate;

FIG. 30 is a cross-sectional view of a structure which allows aplurality of integrated circuits to be temporarily connected to aburn-in board, through a plurality of probe spring contacts;

FIG. 31 is a view of a first step of a spring probe assembly coatingprocess, in which a protective coating is applied to a probe surface ofa spring probe assembly;

FIG. 32 is a view of a second step of a spring probe assembly coatingprocess, in which a layer of photoresistive material is applied to asecond substrate;

FIG. 33 is a view of a third step of a spring probe assembly coatingprocess, in which a coated spring probe assembly is partially dippedinto photoresistive material on a second substrate;

FIG. 34 is a view of a fourth step of a spring probe assembly coatingprocess, in which a coated and partially dipped spring probe assembly isremoved from the second substrate;

FIG. 35 is a view of a fifth step of a spring probe assembly coatingprocess, in which the coated and dipped spring probe assembly is etched,thereby removing the protective coating from portions of the substratenot dipped in the photo-resist;

FIG. 36 is a view of a sixth step of a spring probe assembly coatingprocess, in which photo-resist is stripped from the spring tips on thespring probe assembly, exposing the protective coating;

FIG. 37 is a first perspective view of an alternate probe spring tipcoating process;

FIG. 38 is a second perspective view of an alternate probe spring tipcoating process;

FIG. 39 is a partial cutaway view of an alternate probe spring tipcoating process;

FIG. 40 is a view of a first step of an alternate spring probe assemblycoating process, in which a protective coating is applied to a probesurface of a spring probe assembly;

FIG. 41 is a view of a second optional step of an alternate spring probeassembly coating process, in which a hard mask is applied to a probesurface of a coated spring probe assembly;

FIG. 42 is a view of a third step of an alternate spring probe assemblycoating process, in which the probe spring tips of a coated spring probeassembly are controllably coated;

FIG. 43 is a view of an optional fourth step of an alternate springprobe assembly coating process, in which the uncoated portion of theoptional hard mask layer is removed;

FIG. 44 is a view of an fifth step of an alternate spring probe assemblycoating process, in which the exposed portion of the protective coatinglayer is removed;

FIG. 45 is a view of an optional sixth step of an alternate spring probeassembly coating process, in which remaining coating layer may beremoved from the probe spring tips of the coated spring probe assembly;

FIG. 46 is a view of a seventh step of an alternate spring probeassembly coating process, in which hard mask is stripped from the probespring tips of the coated spring probe assembly; and

FIGS. 47a and 47 b show partial cross-sectional views of reference planelayered spring probe substrates.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a plan view 10 of a linear array 12 of photolithographicallypatterned springs 14 a-14 n, prior to release from a substrate 16. Theconductive springs 14 a-14 n are typically formed on the substrate layer16, by two or more successive layers 17, (e.g. such as 17 a, 17 b inFIG. 47) of deposited metal, such as through low and high energy plasmadeposition processes, followed by photolithographic patterning, as iswidely known in the semiconductor industry. The successive layers 17 a,17 b have different inherent levels of stress. The release regions 18 ofthe substrate 16 are then processed by undercut etching, wherebyportions of the spring contacts 14 a-14 n located over the releaseregion 18, are released from the substrate 16 and extend (i.e. bend)away from the substrate 16, as a result of the inherent stresses betweenthe deposited metallic layers 17 a, 17 b. Fixed regions 15 (FIG. 3, FIG.4) of the deposited metal traces remain affixed to the substrate 16, andare typically used for routing (i.e. fanning-out) from the springcontacts 14 a-14 n. FIG. 2 is a perspective view 22 of a linear array 12of photolithographically patterned springs 14 a-14 n, after release froma substrate 16. The spring contacts 14 a-14 n may be formed in highdensity arrays, with a fine pitch 20, currently on the order of 0.001inch.

FIG. 3 is a side view 26 a of a first photolithographically patternedspring 14 having a short length 28 a, which is formed to define a firsteffective spring angle 30 a, spring radius 31 a, and spring height 32 a,after the patterned spring 14 is released from the release region 18 aof the substrate 16, away from the planar anchor region 15. FIG. 4 is aside view 26 b of a second photolithographically patterned spring 14,having a long spring length 28 b, which is formed to define a secondlarge effective spring angle 30 b, spring radius 31 b and spring height32 b, after the patterned spring 14 is released from the release region18 b of the substrate 16. The effective geometry of the formed springs14 is highly customizable, based upon the intended application. As well,the formed springs 14 are typically flexible, which allows them to beused for many applications.

Patterned probe springs 14 are capable of very small spring to springpitch 20, which allows multiple probe springs 14 to be used to contactpower or ground pads on an integrated circuit device 44 (FIG. 13),thereby improving current carrying capability. As well, for a probe cardassembly having an array 12 of probe springs 14, multiple probe springs14 may be used to probe I/O pads on an integrated circuit device 44under test (DUT), thus allowing every contact 14 to be verified forcontinuity after engagement of the spring contacts 14 to the wafer 92under test, thereby ensuring complete electrical contact between a probecard assembly and a device 44, before testing procedures begin.

Improved Structures for Miniature Springs. FIG. 5 is a first perspectiveview of opposing photolithographic springs 34 a,34 b, having aninterleaved spring tip pattern, before spring release from the substrate16. FIG. 6 is a perspective view of opposing interleavedphotolithographic springs 34 a, 34 b, after spring to substratedetachment.

The interleaved photolithographic springs 34 a, 34 b each have aplurality of spring contact points 24. When spring contacts are used forconnection to power or ground traces 46 or pads 47 of an integratedcircuit device 44, the greatest electrical resistance occurs at thepoint of contact. Therefore, an interleaved spring contact 34, having aplurality of contact points 24, inherently lowers the resistance betweenthe spring contact 34 and a trace 46 or pad 47. As described above,multiple interleaved probe springs 34 may be used for many applications,such as for high quality electrical connections for an integratedcircuit device 44, or for a probe card assembly 60 (FIG. 13), such asfor probing an integrated circuit device 44 during testing.

FIG. 7 is a perspective view 42 of opposing interleavedphotolithographic spring pairs 34 a,34 b in contact with single traces46 on an integrated circuit device under test (DUT) 44. The interleavedspring contact pair 34 a and 34 b allows both springs 34 a and 34 b,each having a plurality of contact points 24, to contact the same trace46. As shown in FIG. 5, when a zig-zag gap 38 is formed between the twosprings 34 a,34 b on a substrate 16, multiple tips 24 are established oneach spring 34 a,34 b. Before the interleaved spring probes 34 a,34 bare released from the substrate 16, the interleaved points 24 arelocated within an overlapping interleave region 36. When the interleavedspring probes 34 a,34 b are detached from the substrate 16, theinterleaved spring points 24 remain in close proximity to each other,within a contact region 40, which is defined between the springs 34 a,34 b. The interleaved spring contact pair 34 a and 34 b may then bepositioned, such that both interleaved spring probes 34 a and 34 bcontact the same trace 46, such as for a device under test 44, providingincreased reliability. As well, since each interleaved spring 34 a,34 bincludes multiple spring points 24, contact with a trace 46 isincreased, while the potential for either overheating or current arcingacross the multiple contact points 24 is minimized.

FIG. 8 is a top view of parallel and opposing single-pointphotolithographic springs 14, before the springs 14 are released from asubstrate 16. As described above for interleaved springs 34 a, 34 b,parallel springs 14 may also be placed such that the spring tips 24 ofmultiple springs contact a single trace 46 on a device 44. As well,opposing spring probes 14 may overlap each other on a substrate 16, suchthat upon release from the substrate 16 across a release region 18, thespring tips 24 are located in close proximity to each other. FIG. 9 is atop view of parallel and opposing parallel single-pointphotolithographic springs 14, after the springs 14 are released from thesubstrate 16, wherein the parallel and opposing parallel single-pointphotolithographic springs 14 contact a single pad 47 on an integratedcircuit device 44.

FIG. 10 is a front view of a shoulder-point photolithographic spring 50,having a point 52 extending from a shoulder 54. FIG. 11 is a partialcross-sectional side view of a shoulder-point photolithographic spring50, in contact with a trace 46 on an integrated circuit device. FIG. 12is a perspective view of a multiple shoulder-point photolithographicspring 50. Single point spring probes 14 typically provide good physicalcontact with conductive traces 46 on an integrated circuit device 22,often by penetrating existing oxide layers on traces 46 or pads 47 by asingle, sharp probe tip 24. However, for semiconductor wafers 92 orintegrated circuit devices having thin or relatively soft traces 46 orpads 47, a single long probe tip 24 may penetrate beyond the depth ofthe trace 46, such as into the IC substrate 48, or into other circuitry.

Shoulder-point photolithographic springs 50 therefore include one ormore extending points 52, as well as a shoulder 54, wherein the points52 provide desired penetration to provide good electrical contact totraces 46, while the shoulder 54 prevents the spring 50 from penetratingtoo deep into a device 44 or wafer 92. Since the geometry of the probesprings 50 are highly controllable by photolithographic screening andetching processes, the detailed geometry of the shoulder-pointphotolithographic spring 50 is readily achieved.

Improved Probe Card Assemblies. FIG. 13 is a cross-sectional view 58 ofa probe card assembly 60 a, wherein a plurality of electricallyconductive probe tips 61 a-61 n are located on a lower probe surface 62a of a substrate 16. A plurality of flexible, electrically conductiveconnections 64 a-64 n are located on the upper connector surface 62 b ofthe substrate 16, and are each connected to the plurality ofelectrically conductive springs probe tips 61 a-61 n, by correspondingelectrical connections 66 a-66 n.

The substrate 16 is typically a solid plate, and is preferably amaterial having a low thermal coefficient of expansion (TCE), such asceramic, ceramic glass, glass, or silicon. The electrically conductivespring probe tips 61 a-61 n establish electrical contact between theprobe card assembly 60 and a semiconductor wafer 92, when the probe cardassembly 60 a and the semiconductor wafer 92 are positioned together.

The spring probe tips 61 a-61 n may have a variety of tip geometries,such as single point springs 14, interleaved springs 34, or shoulderpoint springs 50, and are fabricated on the substrate 16, typicallyusing thin-film or MEMS processing methods, to achieve low manufacturingcost, well controlled uniformity, very fine pad pitches 20, and largepin counts.

The probe tips 61 a-61 n are electrically connected to flexible electricconnections 64 a-64 n, preferably through metalized vias 66 a-66 nwithin the substrate 16. Each of the plurality of flexible electricconnections 64 a-64 n are then electrically connected to a printedwiring board probe card 68, which is then typically held in place by ametal ring or frame support structure 70. The preferred metallized viaelectrical connections 66 a-66 n (e.g. such as produced by MicroSubstrate Corporation, of Tempe, Ariz.), are typically formed by firstcreating holes in the substrate 16, using laser or other drillingmethods. The holes are then filled or plated with conductive material,such as by plating or by extrusion. After the conductive vias 66 a-66 nare formed, they are typically polished back, to provide a flat andsmooth surface.

FIG. 14 is a partial expanded cross-sectional view 79 of a probe cardassembly 60 a, which shows staged pitch and tan-out across a substrate16 and a printed wiring board probe card 68. The probe tips 61 a-61 nare typically arranged on the probe surface 62 a of the substrate, witha fine spring pitch 20. The fixed trace portions 15 are then preferablyfanned out to the metalized vias 66 a-66 n, which are typically arrangedwith a substrate pitch 81. The electrically conductive connections 64a-64 n, which are located on the upper connector surface 62 b of thesubstrate 16 and are connected to the vias 66 a-66 n, are typicallyarranged with a connection pitch 83, which may be aligned with thesubstrate pitch 81, or may preferably be fanned out further on the upperconnector surface 62 b of the substrate 16.

The conductive pads 77 a-77 n on the underside of the printed wiringboard probe card 68 are typically arranged with a pad pitch 85, suchthat the conductive pads 77 a-77 n are aligned with the electricallyconductive connections 64 a-64 n located on the upper connector surface62 b of the substrate 16. The conductive pads 77 a-77 n are thenpreferably fanned out to conductive paths 78 a-78 n, which are typicallyarranged with a probe card pitch 87. The electrically conductiveconnections 72 a-72 n, which are located on the upper surface of theprinted wiring board probe card 68 and are connected to the conductivepaths 78 a-78 n, are typically arranged with a probe card connectionpitch 89, which may be aligned with the probe card pitch 87, or maypreferably be fanned out further on the upper surface of the printedwiring board probe card 68. The probe card connection pitch 89 ispreferably chosen such that the electrically conductive connections 72a-72 n are aligned with the test head connectors 74 a-74 n located onthe test head 76, which are typically arranged with a test head pitch91.

The flexible electric connections 64 a-64 n are typically fabricatedusing a longer spring length 28 than the probe tips 61 a-61 n, toprovide a compliance of approximately 4-10 mils. In some embodiments,the flexible connections 64 a-64 n are typically built in compliance tophotolithographic springs, such as described above, or as disclosed ineither U.S. Pat. No. 5,848,685 or U.S. Pat. No. 5,613,861, which areincorporated herein by reference.

The flexible connections 64 a-64 n are connected to the printed wiringboard (PWB) probe card 68, either permanently (e.g. such as by solder orconductive epoxy) or non-permanently (e.g. such as by correspondingmetal pads which mate to the tips 24 of flexible connection springs 64a-64 n). The printed wiring board probe card 68 then fans out thesignals to pads 72 a-72 n, on a pad pitch 89 suitable for standard pogopin contactors 74 a-74 n typically arranged with a test head pitch 91 ona test head 76.

The flexible connections 64 a-64 n are preferably arranged within anarea array, having an array pitch 83 such as 1.00 mm or 1.27 mm, whichprovides a reasonable density (i.e. probe card pitch 87) for platedthrough-holes (PTH) 78 on the printed wiring board probe card 68, andallows signal fan-out on multiple layers within the printed wiring boardprobe card 68, without resorting to advanced printed wiring board probecards 68 containing blind conductive vias 78 a-78 n.

The flexible conductive connections 64 a-64 n, which contact conductivepads 77 a-77 n on the underside of the printed wiring board probe card68, maintain electrical connection between the printed wiring boardprobe card 68 and the substrate 16, while the substrate 16 is allowed tomove up and down slightly along the Z-axis 84, as well as tilt about itscenter. The flexible connections 64 a-64 n also provide lateralcompliance between a substrate 16 and a printed wiring board probe card68 having different thermal coefficients of expansion (e.g. such as fora low TCE substrate 16 and a relatively high TCE printed wiring boardprobe card 68).

Alternately, the substrate 16 may be an assembly, such as a membraneprobe card, which connects to the printed wiring board probe card 68through membrane bump contacts 64 a-64 n. In alternate embodiments ofthe probe card assembly, connections 64 a-64 n are provided by aseparable connector 132 (FIG. 18), or preferably by a MEG-Array™connector 162 (FIG. 24), from FCI Electronics, of Etters, Pa., whereinball grid solder arrays located on opposing halves of the connector 132,162 are soldered to matching conductive pads on the substrate 16 andprinted wiring board probe card 68, and wherein the conductive pads areeach arranged within an area array pattern, such that the opposinghalves of the connector 132, 162 provide a plurality of matingelectrical connections between each of the plurality of spring probetips 61 a-61 n and each of the plurality of conductive pads 77 a-77 n onthe underside of the printed wiring board probe card 68.

As the size and design of integrated circuit devices 44 becomesincreasingly small and complex, the fine pitch 20 (FIG. 2) provided byminiature spring probe tips 61 a-61 n becomes increasingly important.Furthermore, with the miniaturization of both integrated circuits 44 andthe required probe card test assemblies, differences in planaritybetween an integrated circuit 44 and a substrate 16 containing a largenumber of spring probes 61 a-61 n becomes critical.

The probe card assembly 60 a provides electrical interconnections to asubstrate 16, which may contain thousands of spring probe tips 61 a-61n, while providing adequate mechanical support for the probe cardassembly 60 a, to work effectively in a typical integrated circuit testprobing environment. The probe card assembly 60 a is readily used forapplications requiring very high pin counts, for tight pitches, or forhigh frequencies. As well, the probe card assembly 60 a is easilyadapted to provide electrical contact for all traces 46 (FIG. 7) andinput and output pads 47 (FIG. 7, FIG. 9) of an integrated circuitdevice, for test probe applications which require access to the centralregion of an integrated circuit die 44.

As shown in FIG. 13, the probe card assembly 60 a is typicallypositioned in relation to an a semiconductor wafer 92, having one ormore integrated circuits 44, which are typically separated by sawstreets 94. An X-axis 80 and a Y-axis 82 typically defines the locationof a probe card assembly 60 across a semiconductor wafer 92 or device44, while a Z-axis defines the vertical distance between the surface ofthe wafer 92 and the probe card assembly 60. Position of the wafer 92under test, in relation to the test head 76 and the probe card assembly60 a is required to be precisely located in relation to the X-axis 80,the Y-Axis 82, and the Z-axis 84, as well as rotational Z-axis (i.e.theta) location 90 about the Z-axis 84.

However, it is increasingly important to allow probe card assemblies toprovide contact with a planar semiconductor wafer 92, wherein thesemiconductor wafer 92 and the probe card assembly are slightlynon-planar to each other, such as by a slight variation in X-axisrotation 86 and/or Y-axis rotation 88.

In the probe card assembly 60 a shown in FIG. 13, the probe tips 61 a-61n are flexible, which inherently provides planarity compliance betweenthe substrate 16 and the semiconductor wafer 92. As well, the flexibleconnections 64 a-64 n, which are also preferably flexible conductivesprings 14, 34, 50, provide further planarity compliance between thesubstrate 16 and the semiconductor wafer 92. The probe card assembly 60a therefore provides planarity compliance between a substrate 16 and anintegrated circuit device 44 (i.e. such as by X-axis rotation 86 and/orY-axis rotation 88). As well, the probe card assembly 60 a alsoaccommodates differences in thermal coefficients of expansion (TCE)between the substrate 16 (which is typically comprised of ceramic,ceramic glass, glass, or silicon) and the printed wiring board probecard 68 (which is typically comprised of glass epoxy material).

The signal traces from the probe tips 61 a-61 n, typically having asmall pitch 20, are preferably fanned out to the flexible connections 64a-64 n, typically having a larger pitch, using routing traces on one orboth surfaces 62 a,62 b of the substrate 16.

The flexible connections 64 a-64 n are preferably laid out on astandardized layout pattern, which can match standardized power andground pad patterns (i.e. assignments) on the printed wiring board probecard 68, thus allowing the same printed wiring board probe card 68 to beused for substrates 16 laid out to mate to different integrated circuitdevices 44. As a printed wiring board probe card 68 may be adapted tospecialized substrates 16, for the testing of a variety of differentdevices 44, the operating cost for a printed wiring board probe card 68is reduced.

To aid in high frequency power decoupling, capacitors 172 (FIG. 24),such as LICA™ series capacitors, from AVX Corporation, of Myrtle BeachS.C., are preferably mounted on the top surface 62 b of the substrate16. Alternately, a parallel plate capacitor may be formed within thesubstrate 16, between the reference plane and a plane formed on theunused areas of the routing trace layer. For embodiments in which thesubstrate 16 is composed of silicon, an integral capacitor 67 (e.g. suchas an integral bypass capacitor) may preferably be formed betweenintegral diffusion layers processed within the silicon substrate 16.

A look up and look down camera is typically used to align the waferchuck to the substrate 16, whereby the probe tips 24 are aligned to thecontact pads 47 or traces 46 on a device under test 44 located on asemiconductor wafer 92. Alignment is typically achieved, either bylooking at spring tips 24, or at alignment marks 185 (FIG. 26) printedon the substrate 16.

For prober setups without such a camera, the substrate 16 is preferablycomprised of translucent or transparent material (e.g. such as glassceramic or glass), thereby allowing view-through-the-top alignmentmethods to be performed by a test operator. A window 165 (FIG. 24) ispreferably defined in the printed wiring board probe card 68, whilealignment marks 125 (FIG. 17), 185 (FIG. 26) are preferably located onthe substrate and/or the wafer 92 under test. A test operator may thenuse a camera or microscope to view the alignment marks 125 through thewindow, and align the substrate 16 and wafer 92.

For applications where access to the surface of the semiconductor wafer92 is required while probe contact is maintained (e.g. such as forvoltage contrast electron beam probing during development of theintegrated circuit device 44), a window 123 (FIG. 24) in the substrateregion 16 over the IC center is preferably defined, allowing access toobserve signals in the die 92. Windows 123 work best for integratedcircuit devices 44 having I/O pads located along the die edge, enablingdirect probing of integrated circuit devices 44 located on a wafer 92.Currently, the semiconductor wafer dies 92 must be diced first, whereinseparate integrated circuit devices 44 are wire bonded into a package,and are then tested.

Defined openings (i.e. windows 123) within the substrate 16 are alsopreferably used for in-situ e-beam repair of devices such as DRAMs, inwhich the probe card assembly 60 may remain in place. Testing, repairand retesting may thus be performed at the same station, without movingthe wafer 92.

The structure of the probe card assembly 60 a provides very shortelectrical distances between the probe tips 61 a-61 n and the controlledimpedance environment in the printed wiring board probe card 68, whichallows the probe card assembly 60 a to be used for high frequencyapplications. For embodiments wherein the traces on one or both surfaces62 a,62 b of the substrate 16 are required to be impedance controlled,one or more conductive reference planes may be added within thesubstrate 16, either on top of the traces, below the traces, or bothabove and below the traces. For ultra high-frequency applications, thesubstrate 16 may contain alternating ground reference traces, which areconnected to the one or more reference planes 312 a, 312 b,312 c,312 d(FIG. 47) at regular intervals using vias 316 (FIG. 47), to effectivelyprovide a shielded coaxial transmission line environment 310.

High Compliance Probe Assemblies. As described above, a probe cardassembly structure 60 (e.g. such as 60 b in FIG. 15) fixedly supports asubstrate 16, relative to the printed wiring board probe card 68, in thelateral X and Y directions, as well as rotationally 90 in relation tothe Z axis 84.

While the flexible spring probes 61 a-61 n, as well as flexibleconnections 64 a-64 n, provide some planarity compliance between a probecard assembly 60 and a semiconductor wafer 92 or device 44, otherpreferred embodiments of the probe card assembly 60 provide enhancedplanarity compliance.

Since probe springs 61 a-61 n are often required to be very small, toprovide high density connections and a fine pitch 20, in some probe cardapplications which require substantial planarity compliance, thecompliance provided by the probe springs 61 a-61 n alone may not besufficient. Therefore, in some preferred embodiments of the probe cardassembly 60, the probe card assembly 60 allows the substrate 16 to pivotabout its center (i.e. vary in X-axis rotation 86 and/or Y-axis rotation88), to provide increased planarity compliance to a semiconductor wafer92 under test. In such applications, the probe card assembly 60 muststill exert a controlled downward force in the Z direction 84, forengaging the probe spring contacts 61 a-61 n located on the bottomsurface 62 a of the substrate 16 against a semiconductor wafer 92.

For many embodiments of the probe card assembly 60, the central region119 (FIG. 17) of the substrate 16 is used for electrical connections 64a-64 n between the substrate 16 and the printed wiring board probe card68, thus requiring that the substrate 16 be supported along theperiphery 127 (FIG. 17) of the substrate 16.

A ball joint fulcrum structure may be located within the central regionof a probe card assembly on the back side of the substrate supportstructure, to allow the substrate 16 to pivot about the center, and toprovide force to engage the probe tips 61 a-61 n. However, such astructure would typically impede wire leads or other electricalconnections, which often need to exit over the central region of theprobe card assembly. Moreover, such a movable joint does not typicallyrestrict theta rotation 90 of the substrate 16 reliably.

FIG. 15 is a first partial cross-sectional view 96 a of a bridge andleaf spring suspended probe card assembly 60 b. FIG. 16 is a secondpartial cross-sectional view 96 b of the bridge and leaf springsuspended probe card assembly 60 b shown in FIG. 15, which providesplanarity compliance with one or more integrated circuit devices 44 on asemiconductor wafer 92, which may be non-coplanar with the probe cardassembly 60 b. FIG. 17 is a partial expanded assembly view 124 of majorcomponents for a bridge and spring probe card suspension assembly 60 b.

A leaf spring 98 connects to the substrate 16 through a bridge structure100. The leaf spring 98 and bridge structure 100 provide pivotingfreedom for the substrate 16 (i.e. slight X-axis rotation 86 and Y-axisrotation), with controlled movement in the Z direction 84, X direction80, Y direction 82 and Z-Axis rotation (theta) 90 directions. Inpreferred embodiments, a preload assembly 121 (FIG. 15) is used as ameans for accurately setting the initial plane and Z position of thesubstrate 16 in relation to the printed wiring board probe card 68 b,and to set the pre-load force of the leaf spring 98. For example, in theembodiment shown in FIG. 15 and FIG. 16, the preload assembly 121comprises fasteners 118, which are used in conjunction with bridge shims122. In alternate embodiments, the preload assembly 121 may comprisecalibration screw assemblies or other standoffs 118.

As shown in FIG. 15 and FIG. 16, the outer edges of a leaf spring 99 arefixed to the printed wiring board probe card 68 along its outside edgesby attachment frame 107. The center of the leaf spring 98 is connectedto the bridge 100, by one or more fasteners 108, an upper bridge spacer104, and a lower bridge spacer 106. Bridge preload shims 110 arepreferably added, such as to vary the Z-distance between the leaf spring98 and the bridge 100, which varies the pre-load of the downward forceexerted by the leaf spring 98 on the bridge 100. The bridge 100translates the support from the center out to the corners, and connectsto the substrate 16 by a plurality (typically three or more) bridge legs102. The bridge legs 102 protrude through leg openings 111 defined inthe printed wiring board probe card 68, and are fixedly attached to thesubstrate 16, such as by adhesive or mechanical connections 112.

The leaf spring 98 is typically fabricated from a sheet of stainlesssteel or spring steel, and is typically patterned using chemical etchingmethods. The downward force is a function of the stiffness of thespring, the diameter of the spring spacers 104 and 106, as well as thesize of the leaf spring 98.

While the leaf spring 98 shown in FIG. 16 has the shape of a cross,other geometric shapes may be used to provide downward force, tiltingfreedom, and X, Y, and theta translation resistance. For example, a leafspring 98 having a cross-shape may include any number of wings 99. Aswell, the wings 99 may have asymmetrical shapes, which vary in width asthey go from the outside edge towards the center. Also, the outside edgeof the leaf spring 98 may be connected into a ring, to provide furtherstability of the leaf spring 98.

The bridge 100 and the spacers 104 and 106 are preferably comprised oflight and strong metals, such as aluminum or titanium, to minimize themass of the moveable structure 60 b.

The substrate 16 is typically attached to the legs 102 of the bridge100, using an adhesive 112, such as an epoxy, or solder. Where substratereplaceability is needed, detachable connections 130 such as shown inFIG. 18 can be used.

On the bottom side 62 a of the substrate 16, lower standoffs 114 arepreferably used, which prevent the substrate 16 from touching a waferunder test 92. The lower standoffs 114 are preferably made of arelatively soft material, such as polyimide, to avoid damage to thesemiconductor wafer under test 92. In addition, to further avoid damageto active circuits 44 in the semiconductor wafer 92, the standoffs 114are preferably placed, such that when the probe card assembly 60 isaligned with a device 44 on a semiconductor wafer 92, the standoffs arealigned with the saw streets 94 (FIG. 13) on the semiconductor wafer 92,where there are no active devices 44 or test structures. Furthermore,the height of the lower standoffs 114 are preferably chosen to limit themaximum compression of the spring probes 61 a-61 n, thus preventingdamage to the spring probes 61 a-61 n.

On the upper surface 62 b of the substrate 16, upper standoffs 116 arealso preferably used, to prevent damage to the topside flexibleelectrical connections 64 a-64 n. The upper standoffs 116 are preferablymade of a moderately hard insulative material, such as LEXAN™, silicone,or plastic.

In the preferred embodiment shown in FIG. 15, FIG. 16 and FIG. 17,adjustable bridge screws 118 and bridge shims 122 are used to set theinitial plane of the substrate 16, as well as to provide a downward stopto the substrate 16, so that the flexible connections 64 a-64 n are notdamaged by over-extension.

Since printed wiring board probe cards 68 b are typically made ofrelatively soft materials (e.g. such as glass epoxy), crash pads 120 arepreferably placed on the probe card 68 b, under the adjusting screws118, to prevent the tip of the adjusting screws 118 from sinking intothe printed wiring board probe card 68 b over repeated contact cycles.Fastener shims 122 are also preferably used with the adjusting screws118, such that the initial distance and planarity between the substrate16 and the printed wiring board probe card 68 b may be accurately set.

The preload shims 110 are preferably used to control the initialpre-load of the downward force exerted by the leaf spring 98 onto thebridge 100. The set preload prevents vibration of the substrate 16, andimproves contact characteristics between the substrate 16 and the to thesemiconductor water under test 92.

FIG. 18 is a first partial cross-sectional view 126 a of an alternatebridge and spring suspended probe card assembly 60 c, having anintermediate daughter card 134 detachably connected to the printedwiring board probe card substrate 68 b, and wherein the spring probesubstrate 16 is detachably connected to the bridge structure 100. FIG.19 is a second partial cross-sectional view 126 b of the alternatebridge and spring suspended probe card assembly 60 c shown in FIG. 18,which provides planarity compliance with one or more integrated circuitdevices 44 on a semiconductor wafer 92, which is originally non-coplanarwith the probe card assembly 60 c.

A separable connector 132 is preferably used, which allows replacementof the substrate 16. Substrate attachment fasteners 130 (e.g. such asbut not limited to screws) preferably extend through bridge legs 128,and allow the bridge 100 to be removeably connected to substrate posts128, which are mounted on the upper surface 62 b of the substrate 16.

In one embodiment of the probe card assembly 60, the preferredseparable. connector 132 is a MEG-Array™ connector, manufactured by FCIElectronics, of Etters, Pa. One side of the separable connector 132 istypically soldered to the printed wiring board probe card 68, while themating side is typically soldered to the daughter card 134, whereby thedaughter card 134 may be removeably connected from the printed wiringboard probe card 68 b, while providing a large number of reliableelectrical connections. The daughter card 134 preferably providesfurther fanout of the electrical connections, from a typical pitch ofabout 1 mm for the flexible connections 64 a-64 n, to a common pitch ofabout 1.27 mm for a separable connector 132.

FIG. 20 is a cross-sectional view 136 of a wire and spring postsuspended probe card assembly 60 d. A plurality of steel wires 138 (e.g.typically three or more) allow Z movement 84 of the substrate 16. Thespring post frame 140, which is typically soldered or epoxied to theprinted wiring board probe card 68 c, typically includes one or morespring posts 141, which are preferably used to provide downward Z force,as well as to limit travel.

FIG. 21 is a cross-sectional view 142 of a suspended probe card assembly60 e having an intermediate daughter card 134 detachably connected tothe printed wiring board probe card 68 by a separable connector 132. Theflexible connections 64 a-64 n are preferably made with springs 14, 34,50, and provide both electrical connections to the printed wiring boardprobe card 68, as well as a mechanical connection between the printedwiring board probe card 68 and the daughter card 134. In the probe cardassembly 60 e, the flexible connections 64 a-64 n are permanentlyconnected to conductive pads 143 a-143 n on the daughter card 134, usingeither solder or conductive epoxy. The flexible connections 64 a-64 nare preferably designed to provide a total force larger than thatrequired to compress all the bottom side probe springs 61 a-61 n fully,when compressed in the range of 2-10 mils. As well, the flexibleconnections 64 a-64 n are preferably arranged, such that the substrate16 does not translate in the X, Y, or Theta directions as the flexibleconnections 64 a-64 n are compressed.

Upper substrate standoffs 116 are preferably used, to limit the maximumZ travel of the substrate 16, relative to the daughter card 134, therebyproviding protection for the flexible connections 64 a-64 n. The upperstandoffs 116 are also preferably adjustable, such that there is aslight pre-load on the flexible connections 64 a-64 n, forcing thesubstrate 16 away from the daughter card 134, thereby reducingvibrations and chatter of the substrate 16 during operation. A dampingmaterial 145 (e.g. such as a gel) may also preferably be placed at oneor more locations between the substrate 16 and the daughter card 14, toprevent vibration, oscillation or chatter of the substrate 16.

The separable connector 132 (e.g. such as an FCI connector 132)preferably has forgiving mating coplanarity requirements, therebyproviding fine planarity compliance between the daughter card 134 andthe printed wiring board probe card 68. A mechanical adjustmentmechanism 149 (e.g. such as but not limited to fasteners 166, spacers164, nuts 168, and shims 170 (FIG. 24)) may also preferably be usedbetween the daughter card 134 and the printed wiring board probe card68.

FIG. 22 is a cross-sectional view 146 of a probe card assembly 60 f, inwhich the probe spring substrate 16 is attached to a printed wiringboard probe card 68 through a separable array connector 147. The probecard assembly 60 f is suitable for small substrates 16, wherein a smallnon-planarity between the substrate 16 and a semiconductor wafer undertest 92 can be absorbed by the spring probes 61 a-61 n alone.

FIG. 23 is a cross-sectional view 148 of a pogo wire suspended probecard assembly 60 g, wherein a nano-spring substrate 16 is attached to aprinted wiring board probe card substrate 68 by a large grid array (LGA)interposer connector 150. In one embodiment, the LGA interposerconnector 150 is an AMPIFLEX™ connector, manufactured by AMP, Inc., ofHarrisburg Pa. In another embodiment, the interposer connector 150 is aGOREMATE™ connector, manufactured by W. L. Gore and Associates, Inc., ofEau Clare, Wis. In another alternate embodiment, a pogo pin interposer150 is used to connect opposing pogo pins 152 on the printed wiringboard probe card 68 to electrical connections 66 a-66 n on the substrate16. The substrate 16 is held by a plurality of steel pogo suspensionwires 154, which are preferably biased to provide a slight upward force,thereby retaining the interposer connector 150, while preventingvibration and chatter of the assembly 60 g.

Small Test Area Probe Assemblies. FIG. 24 is a cross-sectional view of asmall test area probe card assembly 60 h, having one or more area arrayconnectors 162 located between the main printed wiring board probe card68 and a daughter card 134, which is attached to a small area springprobe substrate 16.

While many of the probe card assemblies 60 described above provide largeplanarity compliance for a probe spring substrate 16, some probe cardassemblies are used for applications in which the device under testcomprises a relatively small surface area. For example, for applicationsin which a small number (e.g. one to four) of integrated circuits 44 areto be tested at a time, the size of a mating substrate 16 can also berelatively small (e.g. such as less than 2 cm square).

In such embodiments, therefore, the planarity of the substrate 16 to thewafer under test 92 may become less critical than for large surfaceareas, and the compliance provided by the probe springs 61 a-61 n aloneis often sufficient to compensate for the testing environment. While thecompliance provided by the probe springs 61 a-61 n may be relativelysmall, as compared to conventional needle springs, such applications arewell suited for a probe card assembly 60 having photolithographicallyformed or MEMS formed spring probes 61 a-61 n.

The probe card assembly 60 h is therefore inherently less complex, andtypically more affordable, than multi-layer probe card assembly designs.The small size of the substrate 16 reduces the cost of the probe cardassembly 60 h, since the cost of a substrate 16 is strongly related tothe surface area of the substrate 16.

The probe springs 61 a-61 n are fabricated on the lower surface 62 a ofa hard substrate 16, using either thin-film or MEMS processing methods,as described above. Signals from the probe springs 61 a-61 n are fannedout to an array of metal pads 182, 184, 186 (FIG. 26), located on theupper surface 62 b of the substrate 16, using metal traces on one orboth surfaces 62 a,62 b, and conductive vias 66 a-66 n through thesubstrate 16. The top side pads are connected to a daughter card 134,using common micro-ball grid solder array pads, typically at an arraypitch such as 0.5 mm. The daughter card 134 further expands the pitch ofthe array, to pads having an approximate pitch of 0.050 inch on theopposing surface of the daughter card 134. An area array connector 162,such as a MEG-Array™ connector, from FCI Electronics Inc. of Etters Pa.,is used to connect the 0.050 inch pitch pad array to the printed wiringboard probe card 68. Power bypass capacitors 172, such as LICA™capacitors from AVX Corporation of Myrtle Beach S.C., are preferablyadded to the daughter card 134, close to the substrate micro-BGA pads182, 184, 186, to provide low impedance power filtering.

The small test area probe card assembly 60 h preferably includes a meansfor providing a mechanical connection 149 between the printed wiringboard probe card substrate 68 and the daughter card 134. In the probecard assembly 60 h embodiment shown in FIG. 24, one or more spacers 164and spacing shims 170 provide a controlled separation distance andplanarity between the daughter card 134 and the printed wiring boardprobe card substrate 68, while one or more fasteners 166 and nutsprovide a means for mechanical attachment 149. While a combination ofspacers 164, shims 170, fasteners 166, and nuts 168 are shown in FIG.24, alternate embodiments of the small test area probe card assembly 60h may use any combination of means for attachment 149 between thedaughter card 134 and the printed wiring board probe card substrate 68,such as but not limited to spring loaded fasteners, adhesive standoffs,or other combinations of attachment hardware. In some preferredembodiments of the small test area probe card assembly 60 h, themechanical connection 149 between the printed wiring board probe cardsubstrate 68 and the daughter card 134 is an adjustable mechanicalconnection 149, such as to provide for planarity adjustment between theprinted wiring board probe card substrate 68 and the daughter card 134.

Lower substrate standoffs 114, which are typically taller than otherfeatures on the substrate 16 (except for the spring tips 61 a-61 n), arepreferably placed on the lower surface 62 a of the substrate 16,preferably to coincide with the saw streets 94 on a semiconductor wafer92 under test, thereby preventing the wafer under test 92 from crashinginto the substrate 16, and preventing damage to active regions on thesemiconductor wafer 92.

As shown in FIG. 24, the substrate 16 preferably includes an accesswindow 123 (FIG. 17), while the daughter card 134 also preferablyincludes a daughter card access hole 163, and the printed wiring boardprobe card 68 preferably includes and a probe card access hole 165, suchthat access to a semiconductor wafer 92 is provided while the probe cardassembly 60 h is positioned over the wafer 92 (e.g. such as for visualalignment or for electron beam probing). Access holes 123, 163, 165 maypreferably be used in any of the probe card assemblies 60.

FIG. 25 is a top view of a substrate wafer 174, upon which a pluralityof micro ball grid array spring probe contactor chip substrates 16 arelaid out. For spring probe substrates 16 having a small surface area175, several spring probe contactor chip substrates 16 may typically befabricated from a single wafer 174. For example, as shown in FIG. 25, asmany as twenty four sites having a width 176 and a length 178 (e.g. 14mm square), may be established on a standard four inch round startingwafer 174. As well, different substrates (e.g. 16 a, 16 b) may befabricated across a starting wafer 174, whereby the cost of production(which may be significant) for different spring probe substrates 16 maybe shared, such as for masking costs and processing costs. Therefore,the cost of development for different substrates 16 a, 16 b may belowered significantly (e.g. such as by a factor of up to 10 or more).

FIG. 26 is a top view of a single 0.5 millimeter pitch micro ball gridarray 180 for a 14 mm square spring probe contactor chip (NSCC) 16 b.The micro BGA pads 182, 184, 186 are preferably on a standard pitch(e.g. 0.5 mm). The outer five rows of pads 182 and the center pads 184provide 341 signal connections, and the inside two rows 186 provideninety six dedicated power and ground connections. By customizing therouting traces to the spring probes 61 a-61 n, specific power/groundspring positions to match the integrated circuit 44 under test can beaccommodated with a single layer of routing.

Standoffs 114 are preferably placed in locations matching inactiveregions on the wafer 92, such as on the scribe lane 94, to preventdamage to active devices 44 on the device under test 44. One or morealignment marks 185 are also preferably located on the substrate wafer174. The production cost and turnaround time for a probe card assembly60 can be significantly improved, by standardizing the footprints of themicro BGA pad array 180, the daughter card 134, and the printed wiringboard probe card 68. Standardization of the micro-BGA pad array 180, aswell power/ground pad assignments for the pads located on the substrate16 b allows a standardized pattern of vias 66 a-66 n (as seen in FIG.14) in the base substrate 174.

Standardization of other componentry for probe card assemblies 60 oftenallows printed wiring board probe cards 68 (and in some embodimentsdaughter cards 134), to be used for different substrates 16 andintegrated circuit devices 44, wherein only the routing of the substrate16 is customized.

The use of a starting substrate 174 (FIG. 25) having a standardizedpattern of vias 66 a-66 n also allows starting substrates 174 to beordered, stored and used in quantity, thus reducing the cost of startingsubstrates 174, and often reducing the lead time to obtain the startingsubstrates 174.

Alternate Applications for Probe Springs. Photolithographic or MEMSspring probes 61, 14, 34, 50 may alternately be used for bare dieburn-in sockets, such as for DieMate™ burn-in sockets, manufactured byTexas Instruments Inc., of Mansfield Mass., or for Die™Pak burn-insockets, available through Aehr Test, Inc. of Fremont Calif. For baredie burn-in. sockets which contact the substrate 16 around the edges,the probe springs 61 springs and fanout metalization are needed only onone surface (e.g. probe surface 62 a) of the substrate 16. The requiredfanout is used to determine the size of the substrate 16, based on thenumber of the I/O signals needed to be routed to pads on the edge of thesubstrate 16. Alternately, vias 66 in the substrate 16, as describedabove, can be used to route the I/O signals to an array of pads on theopposite surface 62 b of the substrate 16, allowing the substrate to besmaller, and thereby reducing the cost of fabrication.

Tiled Probe Assemblies. FIG. 27 is a plan view 190 of a probe strip tile192, having a probe strip length 198 and a probe strip width 200. Theprobe strip tile 192 has a plurality of probe contact areas 194 a-194 n,each having a plurality of spring probes 61 a-61 n. As well, in theembodiment shown, the spring probes 61 a-61 n are preferably laid out inaligned probe regions 196 a, 196 b (e.g. such as in longitudinallyaligned regions 196 a, 196 b). Use of one or more probe strip tiles 192in a probe card assembly allows simultaneous electrical contact with aplurality of integrated circuit devices 44 (e.g. thereby providing a“one to many” connection), such as for testing adjoining integratedcircuit device sites 44 on a semiconductor wafer 92. The plurality ofprobe contact areas 194 a-194 n are preferably located symmetricallyalong the length and/or width of the probe strip tiles 192, such thatthey align with a symmetrical plurality of integrated circuit devices 44on a wafer 92.

Probe strip tiles 192 may alternately be laid out and used forapplications in which each single probe strip tile 192 provides contactwith a single integrated circuit device site 44 (e.g. thereby providingone or more “one to one” connections), or for applications in which aplurality of probe strip tiles 192 provide contact for an integratedcircuit device site 44 (e.g. thereby providing one or more “many to one”connections).

As well, the probe strip tiles 192, having spring probes 61 a-61 n,typically include electrical vias 66 a-66 n (e.g. such as metalizedvias) and an array of electrical connections 64 a-64 n (FIGS. 1, 17,21), such that while the spring probes 61 a-61 n may typically be laidout to match specific devices 44 under test, the probe strip tiles 192may preferably include standard electrical vias 66 a-66 n and/or arraysof electrical connections 64 a-64 n. For example, in the probe cardassembly 202 shown in FIG. 28 and FIG. 29, each of the probe strip tiles192 includes a standard ball grid array 160 of solder connections.Therefore, while preferred embodiments of probe strip tiles 192 mayinclude spring probes 61 a-61 n which are laid out to match specificdevices 44 under test, the probe strip tiles 192 may be attached tostandardized daughter cards 204 and/or to standardized intermediateconnectors (e.g. such as to a separable connector 132), thus minimizingengineering development costs to produce a tiled probe assembly 202.

FIG. 28 is a partial bottom view of tiled probe head 202 comprising aplurality of probe strip tiles 192 attached to a support substrate 204,which includes an array 207 (FIG. 29) of electrically conductive vias205. FIG. 29 is a side view of a plurality of probe strip tiles 192attached to a probe card, which are used to contact a plurality ofintegrated circuit devices 44 located on a semiconductor wafer 92. Thetiled probe head 202 is typically used to contact a plurality ofintegrated circuit devices 44 located on a semiconductor wafer 92. Theplurality of probe strip tiles 192 are preferably located symmetricallyacross the substrate 204, such that they align with a symmetricalplurality of integrated circuit devices 44 on a wafer 92.

The substrate 204 preferably has a low thermal coefficient of expansion(TCE), and is preferably matched to silicon. As well, the substrate 204typically fans out a large number of signal traces 46, to connectors onthe opposite surface 209 b of the substrate 204. In one embodiment, thesubstrate 204 is a silicon wafer, which includes vias 205 a-205 n (e.g.such as arranged on a 0.056 inch pitch) and thin film routing 46 on oneor both substrate surfaces 209 a, 209 b.

In the tiled probe head 202 shown in FIG. 28 and FIG. 29, the probestrip tiles 192 include groups of probe springs 61 which are used tocontact rows of pads 47 (FIG. 7) on integrated circuit devices 44 havingpads 47 located on opposing sides of a device under test 44 (e.g. suchas on the right and left sides of an integrated circuit device site 44).In the tiled probe head 202 shown, the probe strip tiles 192 arearranged such that one of the probe strip tiles 192 typically contactsthe right side of one circuit device site 44. (e.g. such as using probecontact region 196 a in FIG. 27), in addition to contacting the leftside of a neighboring circuit device site 44 (e.g. such as using probecontact region 196 b in FIG. 27). The embodiment shown in FIG. 28therefore provides simultaneous contact between the plurality of probestrip tiles 192 and a plurality of integrated circuit devices 44, whileallowing adequate tolerances between adjoining probe strip tiles 192,wherein the side edges of the probe strip tiles 192 may preferably beplaced over the saw streets of the integrated circuit device sites 44.For example, saw streets 94 between adjoining devices 44 on a wafer 92may commonly be on the order of 4 to 8 mils wide, thereby providing asimilar gap between probe strip tiles 192 in the tiled probe cardassembly 202. While the illustrative embodiment shown portrays a lineararrangement of probe contact regions, the specific layout is not limitedto the arrangement shown. For example, the tile layer may alternately beused to provide probe connections to any number of IC's, in anyconfiguration.

In alternate embodiments of the tiled probe head assembly 202, all pads47 for an integrated circuit device site 44 may be contacted by probesfrom a single probe strip tile 192.

Burn-In Structures. FIG. 30 is a partial cross-sectional view of aburn-in structure 210 which allows a plurality of integrated circuitdevices 44 to be temporarily connected to a burn-in board 212. Theburn-in board typically includes a variety of circuitry, components, andinterconnections. An array of probe spring (i.e. nano-spring) contactorchips (NSCC) 214 are mounted onto a burn-in board 212, such as by microball grid arrays 216, which provide spring probe electrical connections61 a-61 n between the plurality of integrated circuit devices 44 andexternal burn-in circuitry (not shown). In similar manner to substrate16, as seen in FIG. 14, each of the contactor chip substrates 214 have aconnection surface 62 b, a probe contact surface 62 a, a plurality offlexible electrically conductive probe spring tips 61 a-61 n extendingfrom the probe contact surface 62 a, and a plurality of electricalconnections 66 a-66 n extending through each of the contactor chipsubstrates 214 between each of the flexible electrically conductiveprobe spring tips 61 a-61 n and the connector surface 62 b.

Board vacuum ports 218 are preferably defined in the burn-in board 212,while contactor chip vacuum ports 220 are preferably defined in the NSCCsubstrate 214, wherein the board vacuum ports 218 are generally alignedto the contactor chip vacuum ports 220 (e.g. such that an applied vacuumthrough the board vacuum ports 218 is also applied to the generallyaligned contactor chip vacuum ports 220). An air seal 222 (e.g. such asan epoxy), is preferably dispensed around the periphery of eachnano-spring contactor chip 214, to prevent the loss of applied vacuumthrough the micro BGA ball array 216.

As integrated circuit devices 44 are initially placed on nano-springcontactor chips 214 (e.g. such as by a “pick and place” machine), anapplied vacuum to the board vacuum ports 218 on the burn-in board 212and generally aligned contactor chip vacuum ports 220 on the nano-springcontactor chips 214 prevents the placed integrated circuit devices 44from shifting from their placed positions.

When all of the integrated circuit devices 44 are placed onto thecorresponding contactor chips 214, a clamp plate 224 is preferablyplaced in contact with the integrated circuit devices 44, to retain theintegrated circuit devices 44 in place during burn-in operation.Individual spring pads 226 may also be used, to push on-the integratedcircuit devices 44 under test, to allow for planarity tolerances of theclamp plate 224 and the burn-in board 212. The burn-in structure 210preferably includes means 217 for retaining the clamp plate 224, suchthat once the clamp plate 224 is placed in contact with the integratedcircuit devices 44, the clamp plate 224 is attached to the burn-in board212, and the applied vacuum may be switched off.

Protective Coating Processes for Improved Spring Probes. As describedabove, since spring probes 61 provide advantages of high pitch, high pincount, and flexibility, they may be used for a wide variety ofapplications. However, when these typically small spring probes 61 areused to contact pads 47 on integrated circuit devices 44, such as onsemiconductive wafers 92, wherein the pads 47 often contain an oxidelayer, the spring probes 61 are often required to break through oxidelayers and establish adequate electrical contact with metal traces orconductive pads. As the spring probes 61 are often used many times, thesmall, unprotected spring probe tips 24 may become worn. Therefore, itwould be advantageous to provide an electrically conductive wear coatingon the contact tips 24 of the probe springs 61. However, such aprotective coating is required to cover both the top surface and theside wall surfaces of the spring tip 24.

As described above, the probe springs 61 may be formed by a sputterdeposition and photolithographic process, such as disclosed in U.S. Pat.No. 5,848,685 and U.S. Pat. No. 5,613,861, wherein successive layers ofconductive material are applied to a substrate, and wherein non-planarsprings are subsequently formed. In such processes, however, aprotective coating applied during the deposition process would notinherently provide a continuous coating on all surfaces of the formednon-planar probe springs.

The probe springs 61, after their release, are not planar to thesubstrate surface. Therefore, a protective coating may be applied afterthe springs 61 have been released from the release layer 18. FIG. 31 isa view of a first step 230 of a spring probe assembly coating process,in which a protective coating 232 is applied to a probe surface of aspring probe assembly substrate 16, having one or more non-planar probesprings 61. The spring probe assembly coating process forms a protectivelayer on the non-planar probe springs 61. While the coating process maybe used for a wide variety of non-planar structures, it is specificallyuseful for the processing of thin film and MEMS probe spring contacts61. In FIG. 31, the applied electrically conductive protective coatingis preferably a hard electrically conductive material, such as titaniumnitride, palladium, rhodium, tungsten, nickel, or beryllium copper. Theapplied electrically conductive protective coating is also preferablyrelatively inert or noble material, thereby providing lubricativecharacteristics (i.e. a low coefficient of friction) for the probe tips24 on the spring probes 61. Such materials minimize wear to both devicesunder test and to the spring probes 61, by minimizing galling andoxidation, while reducing the pickup of debris.

When the protective coating 233 is applied 232 to the substrate 16 andprobes 61, the protective coating 233 covers both the planar andnon-planar regions on the exposed surface 62 of the substrate 16. Whilethe spring probes 16 are covered with the protective coating 233 duringthe coating step 230, all the traces on the substrate structure areelectrically shorted together, from the applied conductive coating 233.The conductive coating 233 is therefore required to be patterned, orpartially removed, to restore electrical isolation between differentprobe springs 61 and their respective traces. While conventionalphoto-masking processes are typically used in the majority of integratedcircuit processing, to selectively etch away conductive coatings, suchas titanium nitride coatings, such photo-masking processes are used forplanar structures.

FIG. 32 is a view of a second step 234 of a spring probe assemblycoating process, in which a layer of mask coating material 240 (e.g.approximately 10 microns deep) is applied to a second substrate 236,which preferably has dipping standoffs 238 (e.g. approximately 30microns high). The mask coating material 240 preferably comprises aphotoresistive material 240, or may alternately comprise anothersuitable coating materials 240 (e.g. such as silicone, wax, or epoxy)which are typically used within photolithographic processes. The coatingmaterial 240 is used to protect the applied protective layer 233 onnon-planar portions of the probe springs 61.

FIG. 33 is a view of a third step of a spring probe assembly coatingprocess, in which a coated spring probe assembly is partially andcontrollably dipped 242 into the coating material 240 on the secondsubstrate 236. The depth of applied coating material 240 eventuallycontrols the remaining protective coating 233. The substrate 16 islowered to a desired depth in the coating material 240, which istypically controlled by the applied depth of the coating material 240 onthe second substrate 236, and the height of the dipping standoffs 20.The applied depth may alternately controlled by an operator, such as bycontrolled axial movement of a processing apparatus, to control themovement of the substrate 16 into the photoresistive material 240. Thecoating material may alternately be applied by a variety of techniques,such as the alternate coating process seen in FIG. 37, FIG. 38, and FIG.39.

FIG. 34 is a view of a fourth step of a spring probe assembly coatingprocess, in which a coated and partially dipped spring probe assembly isremoved 246 from the photoresistive material 240 on second substrate 16and cured (e.g. such as by soft baking), leaving a portion of theprotectively 233 coated probe springs 61 covered in a cured coatinglayer 248. FIG. 35 is a view of a fifth step of a spring probe assemblycoating process, in which the coated and dipped spring probe assembly16,61 is etched 250, thereby removing the protective coating 233 fromportions of the substrate 16 (i.e. the field area of the substrate 16)and probe springs 61 not dipped covered in a cured coating layer 248.FIG. 36 is a view of a sixth step of a spring probe assembly coatingprocess, in which cured coating layers 248 are stripped from theportions of the probe springs 61 which were covered in a coating layer248, thereby exposing the protective coating 233.

The non-planar probe spring coating process therefore provides aprotective coating 233 to the tips 24 of the probe springs 61, whileetching the unwanted protective coating in the substrate surface 16 andportions of the spring probes 61 which are not coated with coatinglayers 248.

Alternate Coating Techniques. FIG. 37 is a first perspective view 260 ofan alternate probe spring tip coating process. As described above, asubstrate 16 is provided, having one or more spring probes 61 locatedwithin a region 262 on a surface (e.g. such as probe surface 62 a) ofthe substrate 16, such that spring probes 61 extend from the surface 62.As shown in FIG. 37, wire rods 264, having a rod diameter 267 (FIG. 39),is controllably located on the surface 62 of the substrate 16.

FIG. 38 is a second perspective view 266 of an alternate probe springtip coating process, in which a central region 272 of a cylindricalroller 268, preferably having a uniformly precise roller diameter 270,is applied with a coating 274. The roller diameter 266 is preferablychosen such that the circumference of the cylindrical roller 268 islarger than the length of the substrate 16. FIG. 39 is a partial cutawayview 276 of the alternate probe spring tip coating process shown in FIG.38. The applied coating 274 preferably has a controlled thickness 278 onthe cylindrical roller 268. In some preferred embodiments of thealternate probe spring tip coating process, the cylindrical roller 268is a precision centerless ground roller 268, preferably having adimensional diameter tolerance of ±0.1 mil. While the coating 274 istypically photoresist material, it may alternately be any suitablematerial for controllably masking the probe tips 24, such as silicone orwax material.

As shown in FIG. 38 and FIG. 39, the coated roller 268 is controllablymoved, such as by rolling, across the wire rods 264, whereby the probetips 24, which extend from the surface 62 of the substrate arecontrollably coated with the coating 274. Since the circumference of thecylindrical roller 268 is preferably larger than the length of thesubstrate 16, the applied coating 274 is more uniformly applied acrossthe substrate 16. The alternate coating process 260,266, 276 shown inFIG. 37, FIG. 38, and FIG. 39, respectively, may be used in any of thespring probe assembly coating processes. As well, the alternate coatingprocess 260,266 may be advantageously applied to other coatingapplications.

Alternate Spring Probe Assembly Coating Processes. FIG. 40 is a view ofa first step 280 of an alternate spring probe assembly coating process,in which a protective coating layer 233 (FIG. 41) is applied 232 to aprobe surface 62 a of a spring probe assembly 16, having one or morenon-planar springs 14,61,64. While the alternate coating process may beused for a wide variety of non-planar structures, it is specificallyuseful for the processing of thin film and MEMS probe spring contacts14,61,64.

The protective coating 233 is preferably a hard electrically conductivematerial 286, such as comprising titanium nitride, palladium, rhodium,tungsten, or nickel, and is typically applied 232 by sputter coating orother deposition methods. The applied electrically conductive protectivecoating 233 is also preferably an hard, non-oxidizing and non-gallingmaterial, thereby providing lubricative characteristics (i.e. a lowcoefficient of friction) for the probe tips 24 on the spring probes 61,thus minimizing wear to both devices under test and to the spring probes61.

As described above, when the protective coating 233 is applied 232 tothe substrate 16 and probes 61, the protective coating 233 covers boththe planar and non-planar regions on the exposed surface 62 of thesubstrate 16. While the spring probes 16 are covered with the protectivecoating 233 during the coating step 280, all the traces on the substratestructure are electrically shorted together, from the applied conductivecoating 233. The conductive coating 233 is therefore required to bepatterned, or partially removed, to restore electrical isolation betweendifferent probe springs 61 and their respective traces. Whileconventional photo-masking processes are typically used in the majorityof integrated circuit processing, to selectively etch away conductivecoatings, such as titanium nitride coatings, such photo-maskingprocesses are used for planar structures.

FIG. 41 is a view of a second optional step 282 of an alternate springprobe assembly coating process, in which a hard mask 286 (FIG. 42) isoptionally applied 284 to a probe surface 62 a of a coated spring probeassembly 16. The hard mask 286 is preferably a magnesium, aluminum, ormagnesium oxide hard mask layer 286, and is typically applied 282 bysputter coating or electron beam (i.e. e-beam) evaporation. The optionalhard mask layer 286 is preferably used for applications in which acoating layer 294 (FIG. 43) may not readily adhere to the first probecoat material 233.

FIG. 42 is a view of a third step 288 of an alternate spring probeassembly coating process, in which a portion of the non-planar probesprings 61 (e.g. such as the probe spring tips 24) of a coated springprobe assembly are controllably coated 290 with a coating layer 294(FIG. 43). The coating layer 294 preferably comprises a photoresistivematerial 294 (e.g. approximately 10 microns deep), or may alternatelycomprise another suitable coating materials 294 (e.g. such as silicone,wax, or epoxy) which are typically used within photolithographicprocesses. The coating material 294 is used to protect the appliedprotective layer 233 (and is optionally also used to coat the hard masklayer 286) on non-planar portions of the probe springs 61. The depth ofapplied coating 294 eventually controls the remaining protective coating233. The coating 294 may be controllably applied by a number oftechniques, such as but not limited to dipping (e.g. as shown in FIG.33), or by application of a roller 268 (e.g. such as shown in FIG. 38and FIG. 39). The applied depth may alternately controlled by anoperator, such as by controlled axial movement of a processingapparatus, to control the movement of the substrate 16 into the coatingmaterial 294. The coating layer 294 may also optionally require asecondary curing process, such as but not limited to soft baking, asshown in FIG. 34.

FIG. 43 is a view of an optional fourth step 292 of an alternate springprobe assembly coating process, in which the uncoated portion of theoptional hard mask layer 286 is removed, such as by etching. FIG. 44 isa view of a fifth step 296 of an alternate spring probe assembly coatingprocess, in which the exposed portion of the protective coating layer233 is removed, such as by ion milling. FIG. 45 is a view of an optionalsixth step 298 of an alternate spring probe assembly coating process, inwhich remaining coating layer 294 may be removed from the probe springtips 24 of the coated spring probe assembly 16. However, in manyembodiments of the alternate spring probe assembly coating process, thefifth step 296, which is preferably provided by ion-milling, issufficient to remove the coating layer 294 as well.

FIG. 46 is a view of a seventh step 300 of an alternate spring probeassembly coating process, in which the remaining hard mask 286 isstripped from the probe spring tips 24 of the coated spring probeassembly, thereby exposing the protective coating 233.

The alternate non-planar probe spring coating process therefore providesa protective coating 233 to the tips 24 of the probe springs, whileetching the unwanted applied protective coating 233 in the substratesurface 16 and portions of the spring probes 61 which are not coatedwith coating layer 294.

Spring Probe Substrates for Ultra High Frequency Applications. Asdescribed above, the structure of the probe card assemblies 60 providesvery short electrical distances between the probe tips 61 a-61 n and thecontrolled impedance environment in the printed wiring board probe card68, which allows the probe card assemblies 60 to be used for highfrequency applications. As well, the spring probe substrate 16 maypreferably be modified for ultra high frequency applications.

FIG. 47a shows a partial cross-sectional view 1260 of an ultra highfrequency spring probe substrate 16. For embodiments wherein the traceson one or both surfaces 62 a,62 b of the substrate 16 are required to beimpedance controlled, one or more conductive reference planes 1262 a,1262 b may be added within the substrate 16, either on top of the traces1270, below the traces 1270, or both above and below the traces 1270.The substrate 16 may also contain alternating ground reference traces1266 a, 1266 b, which are connected to the one or two reference planes1262 a, 1262 b, to effectively provide a shielded coaxial transmissionline environment 1268. While the spring probe substrate 16 is typicallya ceramic material, the layer 1264 between reference planes is typicallya dielectric material.

FIG. 47b shows a partial cross-sectional view 310 of an ultra highfrequency spring probe substrate 16. For embodiments wherein a springprobe 61 and related electrical conductors 320, 78, 322 on and throughthe substrate 16 are required to be impedance matched, one or moreconductive reference surfaces 312 a,312 b,312 c,312 d and vias 316 a,316b,316 c may preferably be added, either within or on the substrate 16.As well, the impedance control surfaces 312 a,312 b,312 c,312 d are notlimited to the planar surfaces shown in FIG. 47.

A conductive layer 312 d may be deposited on top of the insulating layer317, to provide a coaxial, controlled low impedance connection.Alternate layers of conductive materials 312 and dielectric materials314 can preferably be integrated within the substrate 16, such as forembodiments which require decoupling capacitors in close proximity to aprobe spring 61. For a substrate 16 which is a conductive material, suchas silicon, a thin oxide layer 318 may preferably be deposited betweenthe substrate 16 and a conductive reference plane 312 c, thereby forminga high capacitance structure 319 between the spring probe 61 and theground planes 312 a and 312 b. As well, one or more assembled components315, such as passive components 315 (e.g. typically capacitors,resistors, and/or inductors), or active component devices 315, may beincorporated on either surface 62 a,62 b of the substrate 16.

The fixed portions 15 of the spring probes 61 typically extend arelatively short distance across the substrate 16. Traces 60 located onthe surface of the substrate 16 are electrically connected to the fixedportions 15 of the spring probes 61, and electrically connect the probesprings 61 to the vias 78. The traces may be comprised of a differentmaterial than the spring probes 61, and are preferably comprised ofmetals having high electrical conductivity (e.g. such as copper orgold).

Although the disclosed probe card assembly systems and improvednon-planar spring probes and methods for production are described hereinin connection with integrated circuit test probes, and probe cards, thesystem and techniques can be implemented with other devices, such asinterconnections between integrated circuits and substrates withinelectronic components or devices, burn-in devices and MEMS devices, orany combination thereof, as desired.

Accordingly, although the invention has been described in detail withreference to a particular preferred embodiment, persons possessingordinary skill in the art to which this invention pertains willappreciate that various modifications and enhancements may be madewithout departing from the spirit and scope of the claims that follow.

What is claimed is:
 1. An apparatus, comprising: a daughter printedwiring board having a bottom surface and a top surface, and a pluralityof electrical conductors extending from the bottom surface to the topsurface; and a substrate having a probe surface and a connector surface,the probe surface having a plurality of spring probe contacts, thespring probe contacts comprising at least two metal layers, the geometryof the spring probe formed by different levels of stress between the atleast two metal layers, the connector surface having a plurality ofelectrically conductive pads, a plurality of electrical connectorsbetween each of the plurality of said spring probe contacts and each ofthe plurality of electrically conductive pads, and a plurality ofelectrical connections between the plurality of electrically conductivepads and the plurality of electrical conductors on the bottom surface ofthe daughter printed wiring board; and a connector comprising aplurality of electrical connections to the plurality of electricalconductors on the upper surface of the daughter printed wiring board,wherein the connector is a separable connector comprising a firstconnector half and a second connector half, the first connector half andthe second connector half forming a removable mating connection betweena plurality of electrical connections on the first half and a pluralityof electrical connections on the second half, the plurality ofelectrical connections on the connector half connected to the each ofthe plurality of electrical conductors on the upper surface of thedaughter printed wiring board.
 2. The apparatus of claim 1, wherein theseparable connector is an area array connector.
 3. An apparatus,comprising: a daughter printed wiring board having a bottom surface anda top surface, and a plurality of electrical conductors extending fromthe bottom surface to the top surfaces; and a substrate having a probesurface and a connector surface, the probe surface having a plurality ofspring probe contacts, the spring probe contacts comprising at least twometal layers, the geometry of the spring probe contacts formed bydifferent levels of stress between the at least two metal layers, theconnector surface having a plurality of electrical conductive pads, aplurality of electrical connectors between each of the plurality of saidspring probe contacts and each of the plurality of electrical conductivepads, and a plurality of electrical connections between the plurality ofelectrically conductive pads and the plurality of electrical conductorson the bottom surface of the daughter printed wiring board; a connectorcomprising a plurality of electrical connections to the plurality ofelectrical conductors on the upper surface of the daughter printedwiring board; a probe card substrate having a top surface and a bottomsurface, and a plurality of electrical conductors extending from the topsurface to the bottom surface, the plurality of electrical conductors onthe bottom surface of the probe card substrate in electrical contactwith the plurality of electrical connections on the connector; and amechanical connection between the daughter printed wiring board and theprobe card substrate; wherein the connector is a separable connectorcomprising a first connector half and a second connector half, the firstconnector half and the second connector half forming a removable matingconnection between a plurality of electrical connections on the firsthalf and a plurality of electrical connections on the second half, theplurality of electrical connections on the first connector halfconnected to each of the plurality of electrical conductors on the uppersurface of the daughter printed wiring board, and the plurality ofelectrical connections on the second connector half connected to each ofthe electrical conductors on the probe card substrate.
 4. The apparatusof claim 3, wherein the separable connector is an area array connector.